1. Field of the Invention
The present invention relates to a solid-state image pickup device including color filters for photographing a color image.
2. Description of the Related Art
A configuration shown in FIG. 4 has been known for a conventional solid-state image pickup device used in a color video camera, a color still-image camera, or the like.
FIG. 4 is a side cross-sectional view illustrating the structure of a pixel of the conventional solid-state image pickup device, in which a photoelectric conversion portion 2 for generating signal electric charges in accordance with the amount of incident light is provided at a portion near the surface of a semiconductor substrate 1. The photoelectric conversion portion 2 is provided for each of a plurality of pixels arranged in the form of a grid. An active device (not shown) is formed on the semiconductor substrate 1 together with the photoelectric conversion portion 2.
A first interlayer insulating film 3, for example, made of SiO2, having an aperture facing the photoelectric conversion portion 2 is deposited on the semiconductor substrate 1, and a first wiring 4 obtained by patterning an Al (aluminum) film or the like to a desired shape is formed on the first interlayer insulating film 3. A second interlayer insulating film 5, a second wiring 6, a third interlayer insulating film 7, and a third wiring 8 are sequentially formed on the first interlayer insulating film 3 in accordance with a circuit pattern.
These interlayer insulating films and wirings do not necessarily have a three-layer structure, but may have a two-layer structure, a single-layer structure or a structure having at least four layers.
A protective film 9, for example, made of SiON is deposited on the third interlayer insulating film 7 so as to cover also the third wiring 8. A first flattening layer 10, for example, made of acrylic resin is deposited on the protective film 9.
A color filter 11 for performing color separation for incident light in accordance with respective pixels is provided on the first flattening film 10. The color filter 11 is formed using a photoresist including pigments of three primary colors, i.e., red (R), green (G) and blue (B).
A second flattening layer 12 having a light transmitting property is deposited on the color filters 11, and a microlens 13, serving as a condenser lens for condensing incident light onto the photoelectric conversion portion 2, is formed on the second flattening layer 12.
As described in Japanese Patent Application Laid-Open (Kokai) No. 5-6849 (1993), in a solid-state image pickup device having a large chip size, since a pattern forming region is larger than an exposable range at a single exposure operation by an exposure apparatus, divided exposure is adopted in which the pattern forming region is divided into a plurality of exposure regions, and a desired pattern is formed by combining divided patterns.
In recent solid-state image pickup devices, a case in which adjacent color filters are formed in an overlapped state or a case in which a gap is produced between adjacent color filters sometimes occurs due to variations in the sizes of color filters or deviations in the positions of color filters as a result of large-scale integration. Furthermore, since corner portions of a color filter have a circular shape due to insufficient resolution of an exposure apparatus, a space where a color filter is not formed is produced at such a corner portion. For example, as disclosed in Japanese Patent Application Laid-Open (Kokai) No. 10-209410 (1998), in order to prevent overlap of color filters and a gap between color filters, there is a method of removing a gap between adjacent color filters by sequentially superposing three types of color filters and then removing upper color filters until the lowermost color filter is exposed.
In this method, however, it is impossible to adjust the thickness of each of the R, G and B color filters in order to adjust differences in light transmittance. Furthermore, it is very difficult to perform a process of removing color filters by performing uniform etching over a large area.
FIG. 5 assumes a case of forming a solid-state image pickup device 14 by dividing it into two exposure regions, i.e., a first exposure region 15 and a second exposure region 16. In this case, as shown in FIGS. 6A and 6B, the amount of overlap and the size of a gap between color filters due to deviations in the positions of color filters sometimes differ between the first exposure region 15 and the second exposure region 16.
In such a case, the surface of the second flattening layer formed on the color filters is not sufficiently flattened, resulting in the formation of projections or recesses at overlapped portions or gap portions among color filters.
For example, as shown in FIGS. 7A and 7B, recesses in the second flattening layer produced at gap portions between color filters disperse incident light by operating in the same manner as lenses. As a result, light passing through a color filter reaches a photoelectric conversion portion, resulting in variations in the amount of incident light among pixels. Furthermore, since light passing through a gap between color filters sometimes reaches a photoelectric conversion portion by being reflected by wirings or the like, a photographed image degrades.
When color filters overlap, the amount of incident light reaching a photoelectric conversion portion decreases because incident light passes through thick color filters, and variations in the amount of incident light occur among pixels.
Particularly, when forming color filters according to the above-described divided exposure, then, as shown in FIGS. 7A and 7B, since the amount of overlap of color filters or the amount of a gap between color filters differ between the first exposure region and the second exposure region, the height of a projection or a recess produced on the surface of the second flattening layer also differs. As a result, pronounced variations in the amount of incident light appear in a photographed image.